fix request start position for chunks larger than 31952 bytes

Author: jeffrson

lib/protocol/SFTP.js

@@ -1986,6 +1986,7 @@ function read_(self, handle, buf, off, len, position, cb, req_) {
   const req = (req_ || {
     nb: 0,
     position,
+    origPosition: position,
     off,
     origOff: off,
     len: undefined,
@@ -2012,7 +2013,7 @@ function read_(self, handle, buf, off, len, position, cb, req_) {
         data = buf;
       else
         data = bufferSlice(buf, req.origOff, req.origOff + req.nb + nb);
-      cb(undefined, req.nb + nb, data, req.position);
+      cb(undefined, req.nb + nb, data, req.origPosition);
     },
     buffer: undefined,
   });